Microscopical study of oculomotor nucleus in human adult. I.

Abstract

The oculomotor nucleus comprise the chief nucleus, the median nucleus, the parasympathetic nucleus, the anteromedial nucleus, the dorsocentral nucleus and the accessory nucleus of the parasympathetic nucleus, the last of my own discovery. The nerve cells in the chief nucleus are represented in their majority by large motor cells provided with many processes and showing virile appearance. The long processes being sometimes double and some-times bifurcated per cell, the total number of the oculomotor root fibres is larger than that of the cells. The short processes apparently end sharply, either unbranched or branched, but their terminal formation is not enough clarified. The cell nucleus is comparatively small and located near the centre of the cells. The cells of the chief nucleus are partially represented by smaller cells, 1/2 to 1/3 in size of the large cells, pear-shaped in form, unipolar or bipolar, with a large cell nucleus, presumably being of vegetative nature. Cells of a third type are extremely few in number. Their size is not much different from the large motor cells, but in form, they are globular and unipolar. They are very similar to the sensory nerve cells found in the nucleus mesencphali n. trigemini, and are without doubt of sensory nature. In the inner and the ventral parts of the fasciculus longitudinalis medialis are found some cells of the same form as the motor cells in the chief nucleus, with which a small number of small vegetative cells are commingled. It seems impossible to divide the chief nucleus distinctly into the various motor centres having each fixed boundary for the outer ocular muscles, because they may be thought diffused over comparatively wide parts, overlapping each other to an extent. The nucleus medianus is inseparable from the chief nucleus at the caudal pats but the boundary between them become more definite as the higher levels are reached. The nerve cells in the basal parts are similar to those in the chief nucleus, but in the upper reaches, more and more bipolar club- or spindle-like cells come into evidence. Also, some smaller cells resembling vegetative nerve cells in the chief nucleus are observable. The cells in the parasympathetic nucleus are small, about 1/3 of the size of the motor cells in the chief nucleus, are unipolar or bipolar, oblong in shape and arranged rather densely in the direction conforming with the arcuate form of this nucleus. Their protoplasm is only weakly stained, their cell nucleus is oversized, and their long processes are represented by minute fibres. Since such minute fibres are also observable in the oculomotor nerve root, I am inclined to give adherence to the proposal that this nucleus is the centre for the pupillar contraction. I have discovered a small group of nerve cells strongly resembling those in the parasympathetic nucleus on the rostrodorsal side between the fasciculus longitudinalis medialis and the chief nucleus. I propose to call this new nucleus the accessory nucleus of the parasympathetic nucleus. The anteromedial nucleus is of the same nature as the nucleus parasym-pathicus, considering the form and the arrangement of the cells. This fact is further evidenced by the union of this nucleus with the parasympathetic nucleus through a cell-bridge containing such cells. The nerve cells in the nucleus dorsocentralis are somewhat smaller than, but similar to, the motor cells in the chief nucleus. In this nucleus, some smaller vegetative cells, as have been found in the chief and the median nucleus, are observable in a small number. Thus, this nucleus also may be assumed to represent one of the oculomotor centres.